20 month old bedtime problems

Hi,My daughter is 20 months old and has always been Angel going to bed. She has gone from 7pm to 8am from approx 6 weeks, and majority of the time she would ask for her bed. The last few weeks however she has not been so good! She literally screams like a toddler being torchured when I put her down and just screams and screams and screams, breaks my heart as I hear she saying 'please mummy' over and over.I have tried leaving her cry it out, I have tried sitting with her, I have tried reading to her, I have tried background noise, I have tried getting in her cot with her, I have tried putting her in my bed....running out of ideas!The only thing that has significantly changed in our household is a new baby, however she is 12 weeks old and the going to bed problem has only been a couple of weeks. She always asks to go in mummy's bed or her sisters bed but cries if I leave her, tonight I tried putting her sisters cot in her room which she said yes to, but the screaming started as soon as I tried to leave!Has anyone else been through anything similar? All and any advice is welcome! Thanks xx